1. Field of the Invention
This invention concerns luminance signal/color signal separator circuits used in devices which process the picture signals of color television receivers, video tape recorders, etc.
2. Description of Related Art
In devices which process the picture signals of color television receivers, video tape recorders (hereafter, VTR), etc., a complex composite signal, in which the luminance signal (hereafter, Y signal) and the color signal (hereafter, C signal) were previously mixed to form the complex composite signal, is used as the video signal. The Y signal and the C signal have to be separated from this type of video signal. This separation is called Y/C separation.
FIG. 3 is a graph of the frequency spectrum of this type of video signal. The vertical axis expresses amplitude, and the horizontal axis expresses frequency. In FIG. 3, the Y signal in the video signal has a frequency spectrum or range of from 0 to about 4.5 MHz. The C signal also has a specified band, referred to herein as the C-band, about a color secondary carrier wave frequency of 3.58 MHz (the secondary carder wave is a substantially pure narrow band signal within the C-band of the spectrum). The Y signal and the C signal have an interleaved relationship, and they are to be separated, spectrum-wise, for example, 1.5 MHz at the low band side of 3.58 MHz and 0.5 MHz at the high band side.
FIG. 4 is a block diagram showing a simple luminance signal/color signal separator circuit which separates the Y signal and the C signal from this type of video signal. In FIG. 4, 41 is an input terminal to which video signal a2 is supplied. Video signal a2 is supplied to band-pass filter (hereafter, BPF) 42 and low-pass filter (hereafter LPF) 43. BPF 42 passes the C-band component of video signal a2 including the color secondary carder wave and all other signals in the C-band frequencies which are present on video signal a2. By this means, BPF 42 extracts and supplies C signal b2 to C signal output terminal 44. LPF 43 passes a low band component of video signal a2 having frequencies lower than the frequencies of the C-band component on video signal a2. By this means, LPF 43 extracts and supplies Y signal c2 to Y signal output terminal 45.
FIG. 5 is a graph showing the C signal b2 output from BPF 42. The vertical axis expresses amplitude, and the horizontal axis expresses frequency. As shown, C signal b2 output from BPF 42 covers the C-band component of video signal a2.
FIG. 6 is a graph showing the Y signal c2 output from LPF 43. The vertical axis expresses amplitude, and the horizontal axis expresses frequency. As shown, Y signal c2 output from LPF 43 covers a low band component of video signal a2 having frequencies lower than frequencies of the C-band component.
When using this type of luminance signal/color signal separator circuit, all frequency components in the original video signal in the frequency range about the C-band component is eliminated from Y signal c2 output from Y signal output terminal 45, and a broad-band luminance signal cannot be obtained. Therefore, Y signal c2 has a narrower spectrum than the original Y signal, and therefore, the horizontal resolution of a display of Y signal c2 is lower compared to a display of the original Y signal when the picture is displayed on a screen. Also, C signal b2 contains those components of the original Y signal having frequency components falling in the C-band about the color secondary carrier wave frequency, those components, constituting noise, remaining as a residual Y signal in C signal b2 output from C signal output terminal 44. This residual Y signal interferes with subsequent signal processing.
FIG. 7 is a block diagram showing a luminance signal/color signal separator circuit which uses a C signal comb filter circuit. In FIG. 7, 51 is an input terminal to which video signal a3 is supplied. Video signal a3 is supplied to BPF 52 and, at the same time, to a first input terminal of subtractor 53. BPF 52 passes the C-band component of video signal a3 including the color secondary wave and all signals in the C-band frequencies which are present on video signal a3. By this means, BPF 52 extracts and supplies C signal b3 to C signal comb filter circuit 54. Comb filter circuit 54 eliminates the residual Y signal from C signal b3 by using Y signal line correlation. Then comb filter circuit 54 supplies purified C signal c3 to a second input terminal of subtractor 53 and, at the same time, to C signal output terminal 55. Subtractor 53 produces purified Y signal d3 by subtracting purified C signal c3 from video signal a3, and supplies purified Y signal d3 to Y signal output terminal 56.
FIG. 8 is a block diagram showing C signal comb filter circuit 54 in FIG. 7. In FIG. 8, 61 is an input terminal to which C signal b3 is supplied from BPF 52. C signal b3 is supplied to "one horizontal scanning cycle" delay circuit (hereafter, 1H delay circuit) 62 and, at the same time, to a first input terminal of subtractor 63. 1H delay circuit 62 delays C signal b3 from input terminal 61 by a 1H delay and supplies this delayed signal to gain control circuit 64 as 1H delay color signal e3. Gain control circuit 64 controls the amplitude of 1H delay color signal e3 and supplies this to a second input terminal of subtractor 63 as gain controlled 1H delay color signal f3. Subtractor 63 produces purified C signal c3 by subtracting gain controlled 1H delay color signal f3 from C signal b3, and supplies this to output terminal 66.
FIG. 9 is a graph showing the gain property of C signal comb filter circuit 54. The vertical axis expresses gain, and the horizontal axis expresses frequency. As shown in FIG. 9, the gain of C signal comb filter circuit 54 takes a comb-shape in frequency.
FIG. 10 is an enlargement along the horizontal axis of portion A in FIG. 9. As shown in FIG. 10, when the frequency of the C signal is an integral multiple of the 1H frequency (i.e., fH=1/1H), the amplitude property of C signal comb filter circuit 54 takes a minimum value. When the frequency of the C signal is a frequency based on fH/2 being added to an integral multiple of the 1H frequency (i.e., fH=1/1H), the amplitude property takes a maximum value.
Thus, a frequency component in a signal input to C signal comb filter circuit 54 having a frequency equal to an integral multiple of the 1H frequency (i.e., fH=1/1H), is attenuated. However, a frequency component of a signal having a frequency equal to fH/2 added to an integral multiple of the 1H frequency (i.e., fH=1/1H) passes through C signal comb filter circuit 54 with hardly any attenuation. For this reason, video signal a3, supplied to input terminal 51 in FIG. 7, is also supplied to the second input terminal of subtractor 53 as purified C signal c3 from which the residual Y signal has been eliminated by passing through BPF 52 and C signal comb filter circuit 54.
FIG. 11 is a graph showing purified C signal c3. The vertical axis expresses amplitude, and the horizontal axis expresses frequency. Purified C signal c3, output from C signal comb filter circuit 54, has a comb type property in which the residual Y signal has been eliminated from the C-band frequencies of signals passing through BPF 52. Subtractor 53 produces purified Y signal d3 by subtracting purified C signal c3 from video signal a3, and supplies purified Y signal d3 to Y signal output terminal 56.
FIG. 12 is a graph showing purified Y signal d3. The vertical axis expresses amplitude and the horizontal axis expresses frequency. Purified Y signal d3, output from subtractor 53, from which the original C signal component (at the color secondary wave frequency) in the C-band frequencies has been eliminated, is in an interleaved relationship with purified C signal c3 shown in FIG. 11. By this means, the luminance signal/color signal separator circuit of FIG. 7 leaves the residual Y signal component within the C-band frequencies in purified Y signal d3. Thus, the band can be sufficiently purified.
When using this type of luminance signal/color signal separator circuit, the Y signal can be sufficiently purified. At the same time, the residual Y signal can be removed from the C signal. However, this construction obtains the Y signal by subtracting the C signal, which has passed through the series connection of a band-pass filter and a C signal comb filter circuit, from a video signal. The BPF is a high-order filter and its gain randomness and phase randomness are large. Thus, it is necessary to accurately control both the gain and phase together with the gain randomness of the C signal comb filter circuit. For this reason, it is difficult to minimize the manufacturing cost of equipment which includes such a luminance signal/color signal separator circuit.
In the above described luminance signal/color signal separator circuit, the band of the luminance signal can be sufficiently purified. At the same time, the residual luminance signal can be eliminated from the C signal. However, the BPF required is a high-order filter, and its gain randomness and phase randomness are large. Thus, it is necessary to accurately control both the gain and the phase together with the gain randomness of the C signal comb filter circuit. As a result, it is difficult to minimize the manufacturing cost of equipment which include this type of luminance signal/color signal separator circuit.
It is an object of the present invention to eliminate the above problem. It is another object to provide a luminance signal/color signal separator circuit which obtains a broad-band luminance signal without the series connection of a band-pass filter and a C signal comb filter circuit and, at the same time, is capable of eliminating any residual luminance signal from the C signal.
In Japanese laid open patent 4-17485 the Y signal is separated from the composite signal by adding a composite signal to a 1H delayed composite signal (since the phase of the C signal is inverted every 1H delay) and the C component remaining mixed in the Y signal is removed by eliminating a specific band of frequencies about 3.58 MHz when the separated C signal has a high saturation level. However, the 4-17485 Japanese laid open patent does not use a band pass filter or disclose the Y signal being extracted by combining a composite signal with a specified C band component of the composite signal.